1. Field of the Invention
The present invention relates to an image information reading apparatus having a reading assembly for applying a stimulating light beam in a main direction to a stimulable phosphor sheet which has recorded thereon radiation image information of a subject and reading photo-stimulated light emitted from the stimulable phosphor sheet in response to the applied stimulating light beam, and an auxiliary scanning system for feeding the reading assembly and the stimulating light beam relatively to each other in an auxiliary direction which is substantially perpendicular to the main direction.
2. Description of the Related Art
There are known systems for either reproducing radiation image information of a subject such as a human body on a photographic photosensitive medium or the like, or outputting the radiation image information as a visible image on a CRT or the like, using a stimulable phosphor which, when exposed to an applied radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet radiation, or the like), stores a part of the energy of the radiation, and, when subsequently exposed to applied stimulating rays such as visible light, emits photo-stimulated light in proportion to the stored energy of the radiation.
Specifically, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet which has a stimulable phosphor layer. When a stimulating light beam such as a laser beam or the like is applied to the stimulable phosphor sheet, the stimulable phosphor sheet emits photo-stimulated light that is commensurate with the recorded radiation image information. The photo-stimulated light is photoelectrically read and converted into an image signal, which is processed to output (reproduce) a visible image based on the radiation image information on a recording medium such as a photographic photosensitive medium or a display unit such as a CRT. Various apparatus which record and output such radiation image information are used in the art.
The above apparatus incorporate a reading assembly which comprises a stimulating system for applying a stimulating light beam to a stimulable phosphor sheet to scan the stimulable phosphor sheet two-dimensionally, and a light collecting system for photoelectrically reading photo-stimulated light emitted from the stimulable phosphor sheet in response to the applied stimulating light beam. In order to read radiation image information carried by the stimulable phosphor sheet with high accuracy, the distance between the stimulating system and the stimulable phosphor sheet, and the distance between the light collecting system, e.g., photoelectric transducers such as CCDs (Charge-Coupled Devices), and the stimulable phosphor sheet need to be set to accurate values.
If the distance between the stimulating system and the stimulable phosphor sheet is varied while the photo-stimulated light emitted from the stimulable phosphor sheet is being read, then the stimulating light beam tends to be brought out of focus on the stimulable phosphor sheet. If the distance between the light collecting system and the stimulable phosphor sheet is varied while the photo-stimulated light emitted from the stimulable phosphor sheet is being read, then the light collecting efficiency changes and the image density varies, failing to obtain the recorded radiation image information accurately. If the above distances remain unchanged, but are too large or too small, then the outputted image suffers an overall quality reduction.
Attempts have heretofore been made to alleviate the above shortcomings. For example, there has been proposed a mechanism (hereinafter referred to as “conventional arrangement 1”) to support one side of a stimulable phosphor sheet on a flat guide plate and nip the stimulable phosphor sheet with a roller or the like to press the stimulable phosphor sheet against the guide plate, thus positionally confining the stimulable phosphor sheet. According to another structure (hereinafter referred to as “conventional arrangement 2”), two paired rollers are disposed one on each side of a position where a stimulating light beam is applied to a stimulable phosphor sheet in a main scanning direction, and the rollers are rotated to feed the stimulable phosphor sheet in an auxiliary scanning direction substantially perpendicular to the main scanning direction.
With the conventional arrangement 1, however, because the stimulable phosphor sheet is held in sliding contact with the guide plate, the stimulable phosphor sheet tends to be smeared and/or damaged, lowering the quality of the image reproduced from the stimulable phosphor sheet and reducing the durability of the stimulable phosphor sheet. The guide plate positioned to support one side of the stimulable phosphor sheet prevents a light collecting system from being positioned on both sides of the stimulable phosphor sheet, but positionally limits the light collecting system to one side of the stimulable phosphor sheet. Consequently, the freedom of the component layout in the apparatus is limited.
With the conventional arrangement 2, since the roller pairs rotate in rolling contact with opposite surfaces of the stimulable phosphor sheet, the stimulable phosphor sheet also tends to be smeared and/or damaged, resulting in the same disadvantages as with the conventional arrangement 1.